com.twitter.finagle.util.CloseNotifier.scala Maven / Gradle / Ivy

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package com.twitter.finagle.util

import com.twitter.util.{Closable, Future, Promise, Return, Time}

/**
 * Allows resources to register their handlers to be invoked when service is closing.
 */
trait CloseNotifier {
  def onClose(h: => Unit)
}

object CloseNotifier {

  /**
   * Creates CloseNotifier that invokes handlers in LIFO order. Methods on
   * created object are NOT thread safe.
   */
  def makeLifo(closing: Future[Unit]): CloseNotifier = new CloseNotifier {
    @volatile private[this] var closeHandlers: List[() => Unit] = Nil

    /**
     * Adds new close handler. If close event already happened,
     * handler is invoked immediately.
     */
    def onClose(h: => Unit) = {
      if (closing.isDefined)
        h
      else
        closeHandlers ::= { () => h }
    }

     // Invokes close handlers in reverse order from which they were added.
    closing ensure { closeHandlers foreach { handler =>
      handler()
    }}
  }

  def makeLifoCloser(): CloseNotifier with Closable = new CloseNotifier with Closable {
    private[this] val closing = new Promise[Unit]
    private[this] val notifier = makeLifo(closing)

    def close(deadline: Time) = { 
      closing.updateIfEmpty(Return(()))
      Future.Done
    }
    def onClose(h: => Unit) = notifier.onClose(h)
  }
}